question

Hi
Not a regex patter/match, but perhaps you don't need the complexity of that. Here is an alternative that may be of use.
Assuming you already have a means to isolate the line you want to check.

         ' EXAMPLE
    
         Dim checkline As String = "8109264F2304300BLA<<<<<<<<<<<6"
    
         Dim result As String = checkline.Substring(7, 1)

Hello LesHay,

Actually I might already found the answer. I just noticed that it's consisted of 7 digits then 1 letter and then again 7 digits so I wrote the following regex:

 var rgxGender = new Regex(@"\d{7}[A-Z]\d{7}");

It seems to be working fine. Of course once I found the match I substring the 8th character as you pointed out. Thank you

A tool like Regex Editor for Visual Studio is really useful for questions like this. Here's my first pass at a RE that matches the value and captures the subset you want. Note that I'm assuming there is only 1 match per line.

regex = new Regex(@"\d{7}(?<letter>[a-z])", RegexOptions.IgnoreCase | RegexOptions.IgnorePatternWhitespace);

var match = regex.Match(input);
if (match.Success)
{
   var letter = match.Groups["letter"]?.Value;
};

In your example there are actually 2 matches within your string input. My regex only covers the portion of the string you mentioned. The foo+ values you weren't specific about so I left them out. If there is a pattern after the letter then you should expand the pattern to encompass that as well.